The acute administration of ethanol decreases cerebral blood flow in the intact animal (see accompanying Project Report "Cerebral Blood Flow and Metabolism in the Rat"). The in vivo effects of ethanol can be studied in more detail with the isolated artery preparation. Studies with isolated arteries have shown: (1) Ethanol induces contractions in isolated arteries, and facilitates the vasoconstrictory effects of norepinephrine. (2) The effects of ethanol appear to be specific for cerebral arteries. (3) Preliminary results suggest that ethanol may interfere with the endothelium-mediated regulation of cerebral vascular smooth muscle tone.